This invention relates to an image processing method and apparatus. More particularly, the invention relates to an image processing method and apparatus for applying image processing to image data transferred from an external device such as a computer.
FIG. 19 is a block diagram illustrating the construction of an image forming apparatus such as a printer for receiving image data possessed by an external device such as a computer and forming an image on a recording medium such as recording paper.
In a printer having a construction of the kind illustrated, image data sent from an external device is received by an interface controller 401 and stored in a frame memory 402 under the control of a memory controller 403. The image data that has been stored in the frame memory 402 is converted to print data by an image generator 404, after which the print data is stored in an output buffer 406. The print data is transferred from the output buffer 406 to a printing unit 407 in synchronism with the operation of the printing unit 407 by control exercised by a printer controller 405, and the printing unit 407 executes printing.
FIG. 20 is a diagram showing the printing operation performed by the printing unit 407. As shown in FIG. 20, the print data is partitioned into units conforming to the recording width (band width) of the recording (printing) head in the printing unit 407. A single image is formed by successively printing the data in these band-width units.
The conventional technique has the following shortcomings:
(1) Applying geometric conversion processing such as enlargement, reduction and rotation to the image transferred from the external device is possible on the side of the image forming apparatus. Processing such as outputting the layout of a plurality of images, pixel operations among a plurality of images and image processing based upon use of a spatial filter may be executed beforehand on the side of the external device, such as a host computer, whereupon it is necessary that the processed data be transferred to the image forming apparatus. However, in a case where an image having a large quantity of data, such as a color image, is processed, a large-capacity external storage device and a high processing speed are required. External devices capable of realizing such processing are limited. PA1 (2) Formats available for the image data include multivalued formats in RGB and CYMK, palette and bitmap formats, etc. In addition, a plurality of formats exist for each category of image. In the prior art described above, image data capable of being transferred between the external device and the image forming apparatus at the time of image formation is of one category only and has only a single format.